426 PEOCEEDINGS OF THE ACADEMY OF [Julv, 



differentiated so-called lung ; therefore these mollusks must come to the 

 surface for air. However, the observations of v. Siebold^ ('59), Pauly*^ 

 (77), Forel ('69, 74, '04), Andre« ('01), Walker ('00) and the experi- 

 ments of Willem ('96) show that the respiration of the animal is in a 

 large part carried on by the outer surface of the body. 



De Varigny's Experiment. — De Varigny noticed that dishes with the 

 largest area contained the largest snails. This at once suggested aera- 

 tion. To determine whether this was the true explanation, he half 

 immersed a small glass cylinder with the bottom covered with muslin 

 in a large vessel of water. To insure the mixture of the water in both 

 vessels, he lifted the small vessel out of the large one daily and allowed 

 it to empty and fill, when he replaced it again. In each vessel he 

 introduced a snail of equal size and age; and at the end of the experi- 

 ment the one that had a large place in which to roam was the larger. 

 As the water in both compartments was in communication, the amount 

 of oxygen in both vessels must be identical. Therefore, the snail 

 having the greatest area to roam about, on his exercise theory, became 

 the larger. 



Willem' s Experiment. — Semper ('79) found that to carry air bubbles 

 through a vessel containing young snails created such a disturbance 

 that the small snails were washed from their substratum. Willem 

 ('96) devised an apparatus for conducting air bubbles through a liquid 

 without disturbing the water. It consisted of a glass tube (fig. 2) (a) 

 immersed in the jar to be experimented on. Below the surface was 

 blown a hole (o). Tube (c), turned upon the end, conducted bubbles 

 of air into tube (a). The bubbles escaped into the water and travelled 

 up tube (a), the water carried up by the bubble escaping by the hole 

 (o), and the air bubble continued up the tube and escaped. 



Willem repeated the experiment of De Varigny, but introduced his 

 aerating apparatus into the small jar (fig. 3). The water, kept con- 

 stantly interchanging in the large and small vessel, caused the snails 

 to be of equal size. 



Vernon ('03) explained the results of this experiment not by lack of 

 aeration, but by the increase of excretory products which did not pass 

 freely through the muslin. 



Surface Aeration. — The experiments undertaken b}" the writer are 

 considered under two heads — surface aeration and artificial aeration. 

 The effect of surface aeration was determined by the use of flat dishes 

 and a battery jar for control. To make the inside area of the jar equal 

 to the inside area of t!ie dish, so as to have equal areas inside the jar 



" Cited from Walter ('06). 



